Plant pathogens, including plant viruses, have a profound impact on agricultural production. Accordingly, the control and eradication of certain plant viruses is of economic importance.
One plant pathogen of economic interest is the potato virus Y. Potato virus Y infects and damages several plant species, including members of the Solanaceae family. In one member of that family, comprising species of potato, infection by potato virus Y may result in as high as an 80% reduction in crop yield. However, despite its name, potato virus Y is pathogenic in a variety of plant species, including non-potato species.
Potato virus Y is a member of the Potyviridae family of viruses, the largest known group (family) of plant viruses. This family, in turn, is comprised of a number of genera, including genius Potyvirus (named after its type member, potato virus Y), genus Baymovirus (type member: barley yellow mosaic virus), and genus Ryemovirus (type member: ryegrass mosaic virus). See generally, Barnett, O. W., Archives of Virology, 118:139-141 (1991); and Reichmnann et al., J. General Virology, 73:1-16 (1992). Significant research has been conducted relating to the genomic structure, organization, and expression of potyviruses. See, e.g., Reichmann et al. (1992). Genomic sequence information is now available for several members of the Potyviridae family. See, e.g., sequences reported in GenBank Accession Nos. M95491, A08776, D00441, X12456 and X97895 (potato virus Y); M38480 and X55802 (potato virus X); X53062 (potato virus M); Z21670 (potato virus A); U19287 (bean common mosaic virus); D83749 and U47033 (bean yellow mosaic virus); X81083, M92280, X56759, D13751 and D00424 (plum pox virus); M96425 (pepper motile virus); X89997, D10930 and D01152 (pea seed-borne mosaic virus); D10927 (turnip mosaic virus); L29569, L31350, and L35588-L35590 (zucchini yellow mosaic virus); X82625 (barley mild mosaic virus); X69757 (barley mosaic virus); Z48506 (brome streak mosaic rymovirus); U05771 and U34972 (peanut stripe virus) U42596 (yam mosaic virus); L38714 (tobacco etch virus); and U38621 (tobacco vein mottling virus), all incorporated by reference herein.
Of interest to the present invention is the P1 gene of viruses of the Potyviridae family, in particular the P1 gene of viruses of the potyvirus genus, especially of potato virus Y. The P1 gene sequence has been reported for a number of different virus species and strains, including those indicated in the preceding paragraph. The Pi gene encodes one of eight functional proteins produced by processing of a primary polyprotein encoded by the 9.7 Kb genome of potato virus Y. See Reichmann et al. (1992). Protein P1 is encoded near the 5' end of the viral genome and is a 35 kDa protein having C-terminal proteolytic activity. Id. The P1 protein also has been reported to bind RNA. Brantley, et al., J. Gen. Virol., 74: 1157-1162 (1993).
Genetically-engineered pathogen-derived resistance to viral pathogens has been achieved in several plant species. For example, resistance to viral infection has been reported in plants transformed with viral coat protein-encoding genes. Hull, et al., Crit. Rev. Plant Sci., 11: 17-33 (1992). Recently, there have been several reports that resistance to a plant virus may be achieved by transforming a susceptible plant with non-structural genes of the virus. However, such attempts have produced relatively strain-specific resistance. For example, strain-specific viral resistance has been reported by transformation of a strain of tobacco with replicase genes of tobacco mosaic virus. Longstaff, et al., EMBO J., 12: 379-386 (1993). Similar strain-specific results in tobacco have been reported by transformation with potato virus Y. Audy, et al., 12 Annual Meeting of the American Society of Virology, University of California at Davis, Calif. 7 (1993). Finally, strain-specific resistance to potato virus Y infection has been reported in tobacco having been transformed with the NIa proteinase of potato virus Y.
To date, methods for introduction of viral resistance in plants, and especially methods for achieving resistance to potato virus Y and other economically-important viruses, have been relatively strain-specific. Moreover, there are no reports of the use of P1 gene sequences to generate resistance to any virus in potatoes or any other plant species. Accordingly, there is a need in the art for a method for conferring resistance to viral pathogens across a range of species. In addition, due to the economic importance of controlling plant pathogens, and especially plant pathogens infecting food crops, there is a need in the art for additional transgenic virus-resistant plant species and methods for making such transgenic plant species.